Methods of reproducing image information in vector form onto a raster pattern of binary pixels are known. They include allocating binary values to the pixels dependent on the position of said pixels with respect to colored and uncolored image areas contained in the image information. See, for example, U.S. Pat. No. 4,593,278.
With the method disclosed therein, image information in vector form supplied by a host processor is rendered suitable for processing by a printer which produces images by successively printing rows of pixels (with values 1 or 0) in consecutive scan lines situated one beneath the other.
The pixel pattern with which this printer works is a square raster in which the pixels occupy fixed positions on the raster points. Lines and boundaries of image parts which extend at an angle other than a right angle to the main directions of the raster are reproduced as follows by the known method: following the scanning sequence of the printer a check is continually made whether a boundary between a first image part and a second image part is approached and, when reached, the last pixel still completely belonging to the first image part is printed in the color (black or white) of that image part, whereafter the next pixel, which is thus intersected by the boundary, is printed in the color of the second image part. Thus a boundary situated obliquely over the pixel raster acquires a step-like configuration, this being visible particularly at small angles between the boundary and the raster direction, and having an adverse effect on the image quality.
Accordingly, it is an object of the invention to provide a method with which, despite the use of a pixel raster of fixed positions, image part boundaries extending obliquely over the raster can be reproduced with greatly reduced step formation.